Bias circuit for a photodetector, and an optical receiver

Abstract

A bias circuit for a photodetector by the present invention provides a bias voltage to the photodetector that performs electric current amplification according to the bias voltage supplied, and is characterized by comprising a power node and an auto-bias circuit that changes a time constant of the bias circuit for the photodetector according to an optical power received by the photodetector, the auto-bias circuit being connected between the power node and the photodetector, thereby reliability of operation of the photodetector is enhanced.

What is claimed is:  
     
       1. A bias circuit for a photodetector to provide the photodetector that performs electric current amplification according to a supplied bias voltage with the bias voltage, comprising: 
       a power node; and  
       an auto-bias circuit which changes a time constant of the bias circuit for the photodetector according to an optical power received by the photodetector, the auto-bias circuit being connected between the power node and the photodetector;  
       wherein the auto-bias circuit comprises first and a second time constants that are switched according to the optical power received by the photodetector; and  
       wherein the auto-bias circuit has the first time constant when the optical power received by the photodetector decreases rapidly, and has the second time constant that is smaller than the first time constant when the optical power received by the photodetector increases rapidly.  
     
     
       2. The bias circuit for the photodetector as claimed in  claim 1 , wherein the auto-bias circuit comprises: 
       a switching device;  
       a first passive device connected in series with the switching device;  
       a second passive device connected in parallel with the switching device; and  
       a grounding node connected to the first passive device.  
     
     
       3. The bias circuit for the photodetector as claimed in  claim 2 , wherein the switching device is a diode. 
     
     
       4. The bias circuit for the photodetector as claimed in  claim 3 , wherein the first passive device is a capacitor, and the second passive device is a resistor. 
     
     
       5. The bias circuit for the photodetector as claimed in  claim 1 , further comprising: 
       a bias control circuit to maintain a magnitude of the bias voltage to be supplied to the photodetector at a constant value, which is connected to a first node between the power node and the photodetector;  
       a resistor connected between the power node and the photodetector; and  
       a capacitor connected to a second node between the power node and the photodetector.  
     
     
       6. An optical receiver comprising a photodetector that performs electric current amplification according to a bias voltage supplied, further comprising: 
       a power node connected to the photodetector,  
       a bias control circuit to maintain a magnitude of the bias voltage supplied to the photodetector to a constant value, which is connected at a first point between the power node and the photodetector; and  
       an auto-bias circuit which changes a time constant of the bias control circuit according to an optical power received by the photodetector, which is only connected to the optical receiver at a second point between the power node and the photodetector and to a circuit ground.